In multi-cylinder engines, typically, a fuel feed system is configured so that a fuel is suctioned by a fuel pump from a fuel tank through a fuel pipe, and is fed through the fuel pipe to a fuel rail forming a part of the fuel pipe. The fuel rail supports fuel injectors corresponding to respective cylinders and distributes the fuel to the fuel injectors.
In some engines, simultaneous expansion occurs. The term “simultaneous expansion” means that a combustion stroke occurs in two or more cylinders substantially simultaneously. The simultaneous expansion has various advantages and has been employed before. When the simultaneous expansion occurs, the amount of the fuel consumed in the two or more cylinders is twice or more as large as that of the fuel consumed when expansion (hereinafter referred to as non-simultaneous expansion) occurs only in a single cylinder.
However, when the fuel is injected in the simultaneous expansion, a pressure within the fuel pipe including the fuel rail is reduced more significantly than in the non-simultaneous expansion, making an engine speed unstable in some cases.